Calendering is a standard process for converting or processing paper that is typically done between the Yankee dryer and the reel section of a conventional tissue machine. In these machines, the area between the Yankee dryer and the reel section of the tissue machine has an open draw where the dried tissue sheet is unsupported. With such an arrangement, a calender section can be inserted into this open area to calender the sheet prior to winding the sheet onto the reel.
More recently, uncreped throughdried tissue machines have been designed in which the dried tissue sheet is carried from the throughdryer to the reel section on a belt or fabric without an open draw. An example of such a machine is described in U.S. Pat. No. 5,593,545 issued Jan. 14, 1997 to Rugowski et al., which is hereby incorporated by reference. In the reel section of such a machine, which is sometimes referred to as a belted reel section, the parent roll of tissue is wound directly against the supporting belt or fabric. As a consequence, there is no open draw area into which a calendering station can be inserted in order to calender the sheet. This can be disadvantageous if a more smooth parent roll tissue surface is desired or if there is a desire to reduce or control the bulk of the sheet or other sheet properties, such as softness, at this point in the process rather than later during converting operations.
Therefore, there is a need for an apparatus and method for calendering a tissue sheet on a tissue machine having a belted reel section.
It has now been discovered that an uncreped tissue sheet, produced on a tissue machine having a belted reel section, can be modified (calendered, embossed, pressed, crimped, printed, chemically treated or otherwise acted upon in a nip between two rolls) while remaining completely supported by either fabrics or rolls. The supporting fabric or fabrics which move the sheet from the throughdryer to the reel section can be the throughdrying fabric or one or more dry end transfer fabrics.
More specifically, in one aspect, the invention resides in a method for modifying an uncreped throughdried tissue sheet supported by a papermaking fabric, said method comprising removing the dried tissue sheet from the papermaking fabric, modifying the tissue sheet, particularly compressively modifying the tissue sheet in a nip between two rolls, and transferring the modified or compressively modified sheet to a papermaking fabric which carries the sheet to a reel section for winding the sheet into a parent roll, wherein the sheet is supported at all times by a roll surface or a supporting fabric. In this aspect of the invention and those described below, any compressive modification step can be carried out between any combination of steel and rubber rolls, such as steel/steel, steel/rubber or rubber/rubber. The rolls can be smooth or engraved, matched or unmatched.
In another aspect, the invention resides in a method for compressively modifying an uncreped throughdried tissue sheet supported by a papermaking fabric, said method comprising removing the dried tissue sheet from the papermaking fabric via a vacuum transfer roll, contacting the sheet with the surface of a rubber-covered backing roll, passing the sheet through a nip between the rubber-covered backing roll and a steel roll, and transferring the compressively modified sheet to a papermaking fabric which carries the sheet to the reel section for winding the sheet into a parent roll.
In another aspect, the invention resides in a method for compressively modifying an uncreped throughdried tissue sheet supported by a papermaking fabric, said method comprising removing the dried tissue sheet from the papermaking fabric, compressively modifying the tissue sheet, and transferring the compressively modified sheet to a papermaking fabric which carries the sheet to the reel section for winding the sheet into a parent roll, wherein, prior to removal of the dried tissue sheet from the papermaking fabric, the dried tissue sheet is sandwiched between the papermaking fabric and a second papermaking fabric, said method further comprising separating the tissue sheet and the second papermaking fabric from the papermaking fabric via a vacuum transfer roll such that the second papermaking fabric is in direct contact with the surface of the vacuum transfer roll, transferring the second papermaking fabric and the tissue sheet to a steel roll such that the tissue sheet is in direct contact with the surface of the steel roll, separating the second papermaking fabric from the tissue sheet, passing the tissue sheet through a nip between the steel roll and a rubber-covered backing roll to compressively modify the sheet, and transferring the compressively modified tissue sheet from the rubber-covered backing roll to the papermaking fabric that carries the tissue sheet to the reel.
In another aspect, the invention resides in a method for compressively modifying an uncreped throughdried tissue sheet supported by a papermaking fabric, said method comprising transferring the dried sheet from the papermaking fabric to a steel roll via a vacuum transfer roll, passing the sheet through a nip between the steel roll and a rubber-covered backing roll, and transferring the compressively modified sheet, via a second vacuum transfer roll, to a papermaking fabric that carries the sheet to the reel.
In another aspect, the invention resides in a method for compressively modifying an uncreped throughdried tissue sheet supported by a papermaking fabric comprising removing the dried tissue sheet from the papermaking fabric, passing the tissue sheet over a support surface, passing the tissue sheet through a nip between a steel roll and a rubber-coated backing roll, passing the resulting compressively modified sheet over a second support surface, and joining the sheet with a papermaking fabric which carries the sheet to the reel section.
In another aspect, the invention resides in a method for compressively modifying an uncreped throughdried tissue sheet supported by a papermaking fabric comprising contacting the throughdried tissue sheet, while still in contact with the papermaking fabric, with a first roll, separating the tissue sheet from the papermaking fabric, passing the sheet through a nip formed between the first roll and a second roll while travelling in a direction opposite the machine direction of travel, transferring the resulting compressively modified sheet to the surface of the second roll and reversing the direction of travel of the sheet while in contact with the second roll, separating the sheet from the second roll and joining the compressively modified sheet with a papermaking fabric that carries the compressively modified sheet to the reel section.
In all aspects of the invention described above and shown in the Figures, the various sheet modification rolls can be calendering rolls, embossing rolls or printing rolls and the like in order to modify the tissue sheet in any desired manner. Calendering rolls can be used to control the caliper of the sheet and improve softness. Embossing rolls, of course, can be used to impart patterns to the sheet. Printing rolls, such as gravure rolls, can be used to print inks or other chemicals, such as softening chemicals, onto the surface of the sheet. Calendering rolls are particularly suitable for compressively modifying the sheet in accordance with this invention.
As used herein, the term xe2x80x9ctissue sheetxe2x80x9d includes paper webs having a basis weight and bulk appropriate for use as facial tissue, bath tissue, paper towels, dinner napkins and the like.
These and other aspects of the invention will be described in greater detail with reference to the drawing.